1. 张思靓, 陶军全 中科院高能所 Sijing Zhang, Junquan Tao (IHEP/CAS)
Search for low mass Higgs-boson like resonances with mh<125 GeV in the diphoton final state at CMS
张思靓, 陶军全 中科院高能所
Sijing Zhang, Junquan Tao (IHEP/CAS)
中国物理学会高能物理分会第十二届全国粒子物理学术会议
2016年8月22-26日 安徽合肥

2. Outline Motivation Lightest scalar Higgs boson h1→ in NMSSM
Searching results from CMS
Interpretation with 2HDM
Summary
J. Fan, JT, G. Chen et al. Chin. Phys. C 38 (2014):
CMS-HIG
G. Cacciapagliaa, S. Le Corre, JT et al. arXiv: 2

3. Motivation
Is the observed 125 GeV scalar at the LHC really the SM Higgs Boson ? Still room for BSM.
Some BSM theories predict modified and extended Higgs sectors, possibly with additional low-mass(<125GeV) scalars/pseudoscalars.
General Two Higgs Doublet Model (2HDM):
2 Higgs doublets → 5 Higgs bosons : h, H, a, H±
4 types of models, main parameters : tan, 
compatible with a 125 GeV SM-like scalar (h or H) + a light Higgs Boson (a or h) in the "alignment limit“
Next-to-Minimal Supersymmetric Standard Model (NMSSM):
2 Higgs doublets + 1 singlet superfields → 7 Higgs bosons : h1, h2, h3, a1, a2, H±
solves the known "-problem" of the simplest SUSY model MSSM
compatible with a 125 GeV SM-like scalar (h1 or h2) + a mostly "singlet-like" light Higgs Boson (a1 or h1)

4. NMSSM scans
Assume the next-to-lightest scalar Higgs boson h2 corresponds to the observed 125 GeV Higgs in LHC, then focus on the lightest Higgs boson h1
Scans with NMSSMTools and the constraints from HiggsBounds and HiggsSignal on h2, and other constraints
Parameter ranges by theoretical and experimental considerations
J. Fan, JT, G. Chen et al. Chin. Phys. C 38 (2014):
Relic density: Ωh2<0.1102
0.1102<Ωh2< (“WMAP" window)
Before constraint on h2 from HiggsBounds and HiggsSignal 4

5. h2 compared with LHC experiments
Compare the h2 signal strength in γγ, ZZ, WW, ττ and bb decay modes with the ATLAS and CMS results: magenta cross for CMS and green for ATLAS in 2013.
Solid : ZZ
Dashed: WW
NMSSM h2 is compatible with the LHC-discovered Higgs boson
h2→VS h2→VV
J. Fan, JT, G. Chen et al. Chin. Phys. C 38 (2014):
h2→VS h2→ττ
h2→VS h2→bb 5 5

6. Lightest Higgs h1 : σ/ σγγSM
J. Fan, JT, G. Chen et al. Chin. Phys. C 38 (2014):
CMS Higgs results
Relic density:
Ωh2<0.1102
0.1102<Ωh2<0.1272
The lightest Higgs h1 signal strength can be enhanced by a factor up to ~3.5 compared to the SM predictions in the mass range 85 to 95GeV 6

7. CMS search with 8 TeV data
We performed the search for new diphoton resonances with mass in the range of [80,110] GeV and with 8 TeV 19.7 fb-1 data .
CMS PAS HIG
Same analysis strategy as the standard CMS H analysis with different kinematic selections
ptlead/mgg>(hltlead+2 GeV)/mmin) = 28/80
pttrail/mgg>(hlttrail+2 GeV)/mmin) = 20/80
|η|< 2.5 but excluding < |η|< 1.566
Eur. Phys. J. C (2014) 74:3076
Events were split into 4 classes to improve the sensitivity, based on the diphoton mass resolution and kinematics MVA used in the standard CMS H analysis 7

8. Signal and background modelling
Parametric signal modelling procedure: a sum of Gaussian functions to fit signal MC at each mass point, for each production process in each of the 4 event classes
Class 0
CMS PAS HIG
Background model fits to data in the 4 event classes: Nth order (N = 4/5 /5/5) of Bernstein polynomial function plus additional double sided Crystal Ball (DCB) function for Z→ee events with both electrons identified as photons
Class 1 8 8

9. Upper limits on σ×BR Observed limit ranges from 40-75 fb
CMS PAS HIG
Statistical treatment for extraction of limits and p-values is the same as that used by all CMS Higgs boson search channels as well as for the combination of channels
Observed limit ranges from fb
Exclude scalars with σ×BR(h) from times the SM 9 9

10. Combined Local p-value
CMS PAS HIG
No significant excess is observed
Maximum significance: ~1.9σ at mH=97.5 GeV 10 10

11. Interpretation with 2HDM
Is CMS 8 TeV h result sensitive to a lighter Higgs in 2HDM?
Reminder: Two doublets - 1 and 2, 5 Higgses - h, H, A, H±
Parameters in the physical basis : mH=125 GeV in our case
4 types of 2HDM : different ways to couple 1 and 2 to fermions : focus on Type I
G. Cacciapagliaa, A. Deandrea , S. Gascon-Shotkin, M. Lethuilliera , S. Le Corre, JT arXiv: (28 Jul 2016)
Extension of 2HDM predictions from gluon fusion and bb production modes in SusHi+2HDMC : VBF/VH production
First comparison of 2HDM with the LHC (CMS) low mass di-photon analysis at 8 TeV

12. A lighter scalar Higgs : Sensitivity
arXiv:
Red points passing the indirect, LEP and LHC Run1 constraints
No sensitivity in the gluon fusion production channel
Many points are above the CMS observed limit in the VBF/VH production mode for light Higgs boson with mass below 105 GeV

13. A lighter scalar Higgs : Constraints
An exclusion zone in the plane tan vs mh in the particular case
Violet points passing the indirect, LEP and LHC Run1 constraints
Orange points are excluded by the CMS low mass di-photon analysis at 95% C.L..
But the exclusion zone depends on the value of the different free parameters.
arXiv:

14. A lighter pseudo-scalar Higgs
Similar kinematic behavior of the two photons coming from a pseudo-scalar particle and a scalar particle
So can directly apply the CMS study as for the scalar case to constrain a possible light pseudo-scalar
Restrict ourselves to Type I only in the gluon fusion production channel
arXiv:
Red points passing the indirect, LEP and LHC Run1 constraints
No sensitivity to a light pseudo-scalar at the LHC Run 1 in the di-photon final state

15. Summary
From NMSSM (Chin. Phys. C 38 (2014): ), signal strength of the lightest scalar Higgs boson h1 can be up to up to a factor ~3.5 compared to SM
Performed the searches for new resonances in  channel (CMS PAS HIG ) in the range of [80,110] GeV with 19.7 fb-1 of data at √s=8TeV: No obvious excess
Interpreted with 2HDM(arXiv: ) : no sensitivity in ggh but VBF/VH
Looking forward to 13TeV results!
Our CMS public 8TeV result
LEP >2σ excess at mH=~98GeV
Phys. Lett. B, 565 (2003):61-75 15 15

16. Thanks for your attention!

17. EXTRA

18. Motivation : Additionally in 2HDM
Additionally, general Two-Higgs-Doublet-Models (2HDM) postulate the existence of additional light Higgs bosons and even admit the possibility that the observed H(125) is only the next-to-lightest Higgs.
2HDM
G. Cacciapaglia et al., arXiv:
Green (light grey) points are all points passing flavour and theoretical constraints
Blue points (grey) are a subset of those which also pass LEP constraints on h1
Red (dark grey) points pass in addition the LHC couplings constraint on h2
So, we extend the CMS data analysis to the low- mass range down to 80 GeV, to search for possible additional Higgs bosons.

19. ATLAS Result Both low- and high-mass extensions to the SM search.
Phys. Rev. Lett. 113,
Both low- and high-mass extensions to the SM search.
Limits on sxBR quoted in fiducial region: ET >22 GeV for both leading and subleading photons, |h| < 2.37 but excluding < |h| < 1.56
No evidence for signal, largest excess <2s at m~80 GeV